Only For Training And Service Purposes - LG KP270 Service Manual

3. TECHNICAL BRIEF
3.17.2 GSM Transmitter
[Figure 3.17.2-1] GSM Transmitter Part Block Diagram
The GMSK transmitter supports power class 4 for GSM850 and GSM900 as well as power class 1 for
DCS1800 and PCS1900. The digital transmitter architecture is based on a very low power fractional-N
Sigma-Delta synthesizer without any external components (see [Figure 3.17.2-1]). The analog I/Q
modulation data from the baseband is converted to digital, filtered and transformed to polar
coordinates. The phase/frequency signal is further on processed by the Sigma-Delta modulation loop.
The output of its associated VCO is divided by four or two, respectively, and connected via an output
buffer to the appropriate single ended output pin. This configuration ensures minimum noise level.
The 8PSK transmitter supports power class E2 for GSM850 and GSM900 as well as for DCS1800 and
PCS1900. The digital transmitter architecture is based on a polar modulation architecture, where the
analog modulation data (rectangular I/Q coordinates) is converted to digital data stream and is
subsequently transformed to polar coordinates by means of a CORDIC algorithm. The resulting
amplitude information is fed into a digital multiplier for power ramping and level control. The ready
processed amplitude signal is applied to a DAC followed by a low pass filter which reconstructs the
analog amplitude information. The phase signal from the CORDIC is applied to the Sigma-Delta
fractional-N modulation loop. The divided output of its associated VCO is fed to a highly linear
amplitude modulator, recombining amplitude and phase information. The output of the amplitude
modulator is connected to a single ended output RF PGA for digitally setting the wanted transmit
power.
LGE Internal Use Only Copyright © 2008 LG Electronics. Inc. All right reserved.
- 56 -

Only for training and service purposes